Hitherto, polyvinyl alcohol-based resins (hereinafter abbreviated as PVA-based resins) have been widely used as materials for dispersants, emulsifiers, suspending agents, fiber processing agents, paper processing agents, binders, adhesives, films, and the like utilizing excellent water solubility, surface properties, adhesiveness, film properties (film-forming ability, strength, oil resistance, etc.). Furthermore, depending on functions required for various uses, modified PVA-based resins into which various functional groups are introduced have been developed. In particular, for improving water resistance which is a big problem for PVA-based resins, numerous modified PVA-based resins have been proposed.
For example, in the case of an acetoacetic ester group-containing PVA-based resin (hereinafter abbreviated as AA-PVA-based resin) wherein an acetoacetic ester group (hereinafter abbreviated as AA group) rich in reactivity is introduced into a side chain of the PVA-based resin, it is known that excellent water resistance is obtained by combined use of a crosslinking agent such as an aldehyde, an amine, or a metal.
As a process for producing such an AA-PVA-based resin, there is known a homogeneous reaction wherein a PVA-based resin is dispersed in acetic acid or is dissolved in an organic solvent such as dimethylformamide or dioxane beforehand and diketene is reacted therewith, but there is required tedious steps such as separation of a reaction product from the solution and solvent treatment and thus the process is economically disadvantageous at industrial production. Therefore, the present applicant has proposed, as convenient and inexpensive processes for producing such an AA-PVA-based resin, a process wherein liquid diketene or diketene gas is directly brought into contact with a PVA-based resin to effect a reaction therebetween (e.g., see Patent Documents 1 and 2) and a process wherein an organic acid is absorbed in a PVA-based resin and then the resulting resin is reacted with diketene (e.g., see Patent Document 3).
Moreover, since such an AA-PVA-based resin is rich in reactivity, viscosity of an aqueous solution thereof is apt to increase depending on storing conditions. As a solution to the problem, there has been proposed an AA-PVA-based resin composition containing specific amounts and specific ratio of an alkali metal acetate salt and acetic acid (e.g., see Patent Document 4).
Furthermore, as uses utilizing characteristic properties of such AA-PVA-based resins, there have been proposed a dispersant for emulsification comprising an AA-PVA-based resin having a block character of 0.6 or less and an average polymerization degree of 500 to 1500 (e.g., see Patent Document 5), a rapid curing adhesive comprising an aqueous liquid containing an AA-PVA-based resin having a block character of 0.3 to 0.6 and an aqueous liquid containing a specific crosslinking agent (honeymoon adhesive) (e.g., see Patent Document 6), a two component adhesive comprising a main agent containing an AA-PVA-based resin and an aqueous emulsion and a curing agent containing a specific amount of a multivalent isocyanate compound (e.g., see Patent Document 7), a heat-sensitive recording medium comprising a resin composition layer containing an AA-PVA-based resin and a cyclic acetal compound having a specific structure (e.g., see Patent Document 8), an ink-jet recording medium wherein an AA-PVA-based resin having a specified maximum value of loss tangent (tan δ) in viscoelasticity is used (e.g., see Patent Document 9), and the like.
Patent Document 1: JP-A-55-094904
Patent Document 2: JP-A-55-137107
Patent Document 3: JP-A-57-040508
Patent Document 4: JP-A-08-302141
Patent Document 5: JP-A-2000-178316
Patent Document 6: JP-A-2002-285117
Patent Document 7: JP-A-2002-356664
Patent Document 8: JP-A-2004-291519
Patent Document 9: JP-A-2003-145918